The next time a major natural disaster strikes in the Asia-Pacific region, the first responders may not be local aid workers or civilian volunteers — they might be American and Japanese combat troops.

Think of it as practicing for battle.

“Disaster assistance is an effective way for the United States and Japan security alliance to demonstrate our dedication to peace, safety, security and the welfare of the region. It is also a great way for us to learn how to work together to better integrate U.S. and Japanese operations,” says retired Lt. Gen. Wallace “Chip” Gregson, former commander of the Okinawa-based III Marine Expeditionary Force.

Aid agencies are calling for the U.S.-Japan alliance to play a greater role in humanitarian assistance and disaster relief operations throughout the Asia-Pacific region. They predict a dramatic increase in the toll from earthquakes, floods and other natural disasters as a result of global warming and rapid population growth, particularly in urban and coastal areas.

Few organizations have the manpower, equipment or training that the military can muster in the immediate aftermath of such events. In the 2011 earthquake and tsunami in northeastern Japan, for example, more than 100,000 Japanese troops and 20,000 U.S. servicemen and women rushed to the region. Scores of warships assembled off the stricken coast and military aircraft were vital in establishing an air bridge for aid workers and supplies.

More than 20,000 people were killed and hundreds of thousands were left homeless. In the 2004 tsunami in Indonesia, 230,000 were killed and countless were left without food, water or shelter.

“About 50 percent of all natural disasters happen in the Asia-Pacific region, and people turn to Japan and the U.S. for help, so we have to strengthen our preparedness and response,” says Charles Aanenson, chief executive officer of Peace Winds America, which is pushing for a greater military role in disaster response.

“There already is an extremely effective communication between the Japan Self Defense Forces and U.S. Forces-Japan, and what we envision is expanding that throughout the region,” Aanenson says.

That’s seems to be fine with military leaders. Though outwardly benign, disaster relief missions can provide critical, real-world training opportunities. That’s particularly important now. The U.S. defense budget is shrinking and Japan’s armed services operate under strict constitutional restraints, even as China’s military grows rapidly in strength and assertiveness.

The 2011 disaster provided important lessons for U.S. and Japanese troops.

Joint headquarters were established in Tokyo and liaison officers were assigned to major units in the field. The Americans rushed specialized troops and equipment to re-open the Sendai airport — a critical transportation hub buried under six feet of mud and debris — and used Marine Corps amphibious assault vehicles to shuttle victims, aid workers and supplies from ship to shore.

The Japan Self Defense Force (JSDF) took the lead in searching for victims, restoring ground transportation and providing food, water and shelter for survivors. American and Japanese troops often worked side by side in tough winter conditions.

“It may seem tenuous, but the benefits of humanitarian assistance and disaster relief (HA/DR) operations for potential combat capabilities are very real. Logistics, communication and intelligence cooperation and coordination are the basis for successful combat operations, and those are the core of HA/DR operations, as well,” says Garren Mulloy, a former British Army officer who now teaches international relations at Tokyo’s Daito Bunka University.

The overall success of the operation was not lost on the Japanese public, or leaders. The approval rating for the JSDF climbed to 91 percent, a post-war high. Eighty-two percent of Japanese described having “friendly feelings” toward the United States, also a record high.

Under Japan’s pacifist constitution, HA/DR has long been a primary domestic mission for the JSDF. But increasingly leaders view overseas missions, particularly in partnership with the Americans, as a way to provide troops with real-world experience without generating fear of renewed Japanese militarism.

“Disaster relief cooperation is benign and harmless. This is a good way to engage the region in pursuing improved relations,” says retired Lt. Gen. Noboru Yamaguchi, former head of the Japan Ground Self Defense Force’s Research and Development Command.

Maybe so, but uniformed foreigners are not always welcome, even when they mean well. Indonesia gratefully accepted American help following the 2004 tsunami, but refused to allow Navy or Marine helicopters to remain ashore overnight. Instead, those aircraft were required to fly back to U.S. warships offshore; the ships themselves were required to remain outside Indonesia’s 12-mile territorial limit.

China, too, was quick to accept Japan’s offer of a civilian search and rescue team and $60 million worth of relief supplies after the 2008 earthquake in Sichuan Province. But Chinese authorities insisted the team and supplies arrive by private charter plane rather than Japanese military aircraft.

Mulloy says that any increase in cooperation between U.S. and Japanese military forces in disaster relief — no matter how well-intentioned — will be viewed by at least one neighbor as a veiled attempt to bolster Japan’s military.

“China will see a hidden agenda,” says Mulloy. “No matter how innocuous it might appear, HA/DR cooperation, particularly in East Asia, is seen as part of the broader security context.”

Spitzer is a veteran journalist and defense correspondent, based in Tokyo. He has covered nearly every major U.S. military deployment since Operation Desert Shield and Desert Storm and has made more than a dozen reporting trips to Iraq and Afghanistan.